[code-reflection] Integrated: Added field store and load to JavaCodeBuilder

[Gary Frost]

Added field load and store to JavaCodeBuilder. 

Also added config bit SHOW_COMPUTE_MODEL_JAVA_CODE

For example 

java @.run ffi-opencl -DHAT=MINIMIZE_COPIES,SHOW_COMPUTE_MODEL_JAVA_CODE  life

To show a java representation of the compute model before injecting buffer tracking

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Commit messages:
 - Added field store and load to JavaCodeBuilder

Changes: https://git.openjdk.org/babylon/pull/819/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=819&range=00
  Stats: 65 lines in 7 files changed: 37 ins; 14 del; 14 mod
  Patch: https://git.openjdk.org/babylon/pull/819.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/819/head:pull/819

PR: https://git.openjdk.org/babylon/pull/819